Since a large current of several thousand amperes or more flows in the generator during operation, the generator is cooled typically using a refrigerant such as air, hydrogen, and water, in order to prevent overheating. Without cooling, the temperature would rise by at least 100° C. or more, deteriorating a resin material included in the generator, which causes a failure. For this reason, the cooling is a very important technique.
Here, a structure of a conventional stator coil of a generator will be described.
FIG. 4 is a cross-sectional view illustrating a stator coil 10 of a generator according to a conventional technique. As illustrated in the figure, a wire insulation layer 12 is formed on the outer circumferential surface of a wire 11. Four wires 11, each covered with the wire insulation layer 12, form a wire bundle. Formed on the outer circumferential surface of this wire bundle (portions of the wire insulation layers 12 corresponding to the outer circumferential surface of the wire bundle) is an interlayer insulation layer 13.
A wire group is formed by four wire bundles juxtaposed together, each bundle having the interlayer insulation layer 13 formed thereon. Formed on the outer circumferential surface of this wire group (portions of the interlayer insulation layers 13 corresponding to the outer circumferential surface of the wire group) is a main insulation layer 14.
Formed on the outer circumferential surface of the main insulation layer 14 is an outer-layer insulation layer 15. The outer-layer insulation layer 15 protects the main insulation layer 14 from dust, moisture, voltage between coils, and the like.
A mica tape is generally used for an insulation layer such as the main insulation layer 14 of the stator coil 10. The mica tape is a tape in which glass fiber or resin material is used as a base material, which is dredged with mica powder and pasted together with adhesive. Since mica has an excellent insulation property, the use of a mica tape reduces the amount of coil insulation material.
Next, descriptions will be provided with reference to Patent Documents 1 and 2 for a conventional cooling method for a coil of a rotating electrical machine such as a generator.
Note that a portion of a coil positioned inside an iron core (inside slots formed in the iron core) is referred to as a coil side portion, and a portion of the coil positioned outside the iron core (outside the slots formed in the iron core) is referred to as a coil end portion.
As for how to improve the cooling performance of the coil side portion of a coil, as indicated in Patent Document 1 (Japanese Patent No. 5159812), an insulation material having high thermal conductivity is used as a material of an insulation layer of the coil side portion to improve the cooling performance.
On the other hand, as for the cooling of the coil end portion, as indicated in Patent Document 2 (Japanese Patent Application Publication 2012-100458), it is common to control the flow of the refrigerant to improve the cooling performance.
Since the coil end portion is not in contact with a metal (iron core), and in addition, has a problem that the adhesion between the coil insulation materials is poor, which tends to cause a gap, the cooling performance cannot be improved so much even if an insulation material having a high thermal conductivity is used at the coil end portion. For this reason, to cool the coil end portion, the coil end portion is adapted to be exposed efficiently to the refrigerant by controlling the flow of the refrigerant.